This invention relates to the field of machine vision, and more specifically to a method and apparatus of obtaining three-dimensional inspection data for manufactured parts (such as disk-drive suspension assemblies) in a manufacturing environment.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings hereto: Copyright (copyright) 1998-2000, PPT Vision, Inc., All Rights Reserved.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings hereto: Copyright (copyright) 1998-1999, PPT Vision, Inc., All Rights Reserved.
There is a widespread need for inspection data for electronic parts in a manufacturing environment. One common inspection method uses a video camera to acquire two-dimensional images of a device-under-test.
Height distribution of a surface can be obtained by projecting a light-stripe pattern onto the surface and then re-imaging the light pattern that appears on the surface.
One technique for extracting this information based on taking multiple images (three or more) of the light pattern that appears on the surface while shifting the position (phase) of the projected light stripe pattern is referred to as phase shifting interferometry, as disclosed in U.S. Pat. Nos. 4,641,972 and 4,212,073 (incorporated herein by reference).
The multiple images are usually taken using a CCD (charge-coupled device) video camera with the images being digitized and transferred to a computer where phase-shift analysis, based on images being used as xe2x80x9cbuckets,xe2x80x9d converts the information to a contour map (i.e., a three-dimensional representation) of the surface.
The techniques used to obtain the multiple images are based on methods that keep the camera and viewed surface stationary with respect to each other while moving the projected pattern.
One technique for capturing just one bucket image using a line scan camera is described in U.S. Pat. No. 4,965,665 (incorporated herein by reference).
U.S. Pat. Nos. 5,398,113 and 5,355,221 (incorporated herein by reference) disclose white-light interferometry systems which profile surfaces of objects.
In U.S. Pat. No. 5,636,025 (incorporated herein by reference), an optical measuring system is disclosed which includes a light source, gratings, lenses, and camera. A mechanical translation device moves one of the gratings in a plane parallel to a reference surface to effect a phase shift of a projected image of the grating on the contoured surface to be measured. A second mechanical translation device moves one of the lenses to effect a change in the contour interval. A first phase of the points on the contoured surface is taken, via a four-bucket algorithm, at a first contour interval. A second phase of the points is taken at a second contour interval. A control system, including a computer, determines a coarse measurement using the difference between the first and second phases. The control system further determines a fine measurement using either the first or second phase. The displacement or distance, relative to the reference plane, of each point is determined, via the control system, using the fine and coarse measurements.
Current vision inspection systems have many problems. Among the problems are assorted problems associated with the mechanical translation devices used with the vision inspection systems to handle the devices under inspection. One problem is that vision systems typically take up a large amount of linear space on a manufacturing line. Typically small devices, such as disk-drive suspensions, are placed in standard trays, to facilitate the handling of the small devices. In other cases, the disk-drive suspensions are manufactured from a continuous strip of thin metal, wherein at least a portion of the strip is maintained, with other portions cut away to form the suspensions, thus leaving the suspensions attached to the remaining strip. The suspensions can bend at various angles relative to the strip they are attached to. This strip is then used to facilitate the handling of the suspensions, such as positioning the suspensions under a machine-vision head at an inspection station. The exact positioning of the suspensions in their trays, or their relative orientation to the strip can vary, putting demands on the machine-vision system to determine the orientation and angle of the parts relative to the machine-vision head.
To overcome the problems stated above as well as other problems, there is a need for an improved machine-vision system and more specifically for a mechanical apparatus and method for inspecting manufactured parts such as disk-drive suspensions, and for determining various heights, dimensions, and angles of the parts.
In the context of a machine-vision system for inspecting a part, this invention includes method and apparatus to provide high-speed 3D (three-dimensional) inspection of manufactured parts. In some embodiments, precision stamped, formed, and/or laser-cut metal parts are inspected to obtain dimensional and geometric information regarding such characteristics as sag or bow of subportions of the item, the angle of pitch, yaw, and/or roll of one portion relative to another, heights of various formations on the part.
One aspect of the present invention provides a machine-vision system for inspecting an object. This system includes a light source, an imager, and a computer. The light source provides projected patterned light on the object useful to obtain 3D geometric information about the object. The imager has a reception optical axis that intersects the object when the machine-vision system is in operation. In some embodiments, the imager includes at least three rows of imaging pixels positioned to receive light shone onto the object by the light source. Computer system calculates three-dimensional object-geometry data of the object using signals from the imager, and computes at least a first characteristic plane and a second characteristic plane of the object from the calculated object-geometry data.
In some embodiments, the machine-vision system further includes an inspection station that supports the object, a scanner mechanism, an isolation mount, and a machine base The scanner mechanism moves the imager relative to the object at the inspection station such that different portions of the object are successively imaged by the imager The machine base supports the inspection station and the scanner mechanism. The isolation mount is located between the machine base 410 and the inspection station to reduce coupling of vibration between the machine base and the inspection station. In some embodiments, the scanner mechanism 408 and the inspection station are affixed to one another more rigidly than either is to the machine base. In some embodiments, the isolation mount also provides vibration dampening.
Another aspect of the present invention provides a method of measuring a three-dimensional geometry of an object having at least one surface to be measured. The method includes receiving image signals representing a three-dimensional geometry of the object into a computer, calculating with the computer object-geometry data representing three-dimensional geometry of the object, and calculating with the computer values representing at least a first characteristic plane and a second characteristic plane of the object from the calculated object-geometry data.
Yet another aspect of the present invention provides a machine-vision system for inspecting an object that includes a light source that provides projected light on the object and an imager, wherein the imager generates signals from the light representative of three-dimensional object-geometry data of the object. In some embodiments, the system includes means for determining at least a first characteristic plane and a second characteristic plane of the object from the image signals. In other embodiments, system includes means for determining an angle between a first characteristic plane and a second characteristic plane of the object from the image signals. In other embodiments, system includes means for determining a distance between a first feature of the object and a first characteristic plane and the distance between a second feature of the object a second characteristic plane of the object from the image signals.